Radioactive test circuit



Jan. 19, 1954 Filed Dec. 29, 1949 2 Sheets-Sheet 1 A k/ 5O 80 En 4%; A l BI as INVENTOR.

IAN MCLAREN yCARL E.AL5TERBERG- M \em ATTORNEY Jan. 19, 1954 Filed Dec. 29, 1949 H. M LAREN ETAL 2,666,857

RADIOACTIVE TEST CIRCUIT 2 Sheets-Sheet 2 INVENTOR. m/v H. McLAREN a y CARL E ALSTERBERG ATTORNEY Patented Jan. 19, 1954 UNITED STATES Aren't OFFICE! berg,v Detroit, Mich assignors to Bendix Aviantion Corporation, Detroit; Mich, a corporation oiDelaware Application December 29, 1949; SerialN'o". 138;!)62

& Claims; i

This invention relates to electrical circuits'and more particularly to circuitsfor testing the oper ation of a system for measuring the amount of radioactivity in a particular locality.

In our co-pending application Serial No. 138,769 filed January 1950, we: have disclosedan electrical system for measuring radioactivity. This particular system is adapted to measure: a. wide range of radioactivity and to' provide a visual aid for instantaneously indicating the generallevel of radioactivity present. Thesystem operates upon the principle of employing an ionization chamber to convert theradiations-into a: measurable electric current, then ampliiying the current and passing it through a calibrated indicator.

In order to be: assured that. the above system is operating properly and that the meter is correctly calibrated, a test-specimen having aknown amount of radioactivity is provided in a test circuit- The circuit maintains the radioactive specimen out of the field of the ionization chamher until a calibration measurement is desired. Then the circuit operates to rotate the specimen through a predetermined are into thefield of the ionization chamber.

An object of this invention is to provide an electrical circuit for checking the operationof a system for measuring the amount of radioactivity in a particular locality.

Another object of this invention is to provide an electrical circuit of theabove character which is simple in construction, efficient and reliable in operation.

Still another object is to provide an electrical circuit of the above indicated character adapted to rotate a specimen having a known radioactivity through a predetermined are into the fieldof an ionization chamber so. that a calibrating measurement may be obtained.

Other objects and advantages" of the" invention will be-apparent from a moredetailed description of the invention and from the appended drawings and claims.

In the drawings:

Figure 1 is a diagram of an electrical test circuit for calibrating the measurements of an electri'cal system for measuring the amount of radioactivity in a particular locality;

Figure 2 is a block diagram of an electrical system which measures radioactivity;

Figure 3 is a iront-elevational' view of the testingapparatus with some of the; parts broken away toshow other parts. in detail;

' Figure4 is a sectional view taken substantial l'y along the line 7 4-4 I of Figure 3 and Figure 5' is a schematic diagram illustrating anotherelectrical test circuit for calibrating the measurements of the system shown in Figure 2.

Inone of the embodiments of the invention, a test specimen Ill CFigure 4) having a known amount of radioactivity is provided to check the operation: oi asystemfor measuring the amount of radioactivity penetrating anionization cham-- ber', generallyindicated at 4 Figu-re 2.) The ionization chamber preferably has cylindrical metallic walls serving as a positive terminal 5 and an axially disposed metallic rod serving as: a negative terminal 16 therod being suitably insulated from the cylinder itself; Gamma rays penetrate: the walls of the ionization chamber and produce electrons and positive ions ina suit;- able gas. such. as argon,- se'aled within the: chanther; The electrons flow to terminal I25 and the: ions to terminal [6 and produce a currentihrougha-detector IT. The current isampli-fied by an. amplifier l8 before it is introduced to an indicator I 9.

The: indicator 19': has: a plurality of: scales each ozti which measures: a different range of radio activity; Thus, one: scale 20: may measure 0-0-11 roentgens per-'zaehourdamanother scale 21 O"-0.5 roentgens per 24-hour day; and a third scale: 22 (l -50 roentgensperf 24-hourday. Each. scale hasa different color: and is. associated with a bulb 2 51 which has the. same: color.. When illuminated; eachbulb providesa visual aid-1 for instantaneously indicatingv the particular scale which. should: be read, as disclosed: in. co-p'ending application Serial No- 1383061,. filed December 29, 19.49,. by Fred N. Blackmore and Donald F.. Clinton and ctr-pending: application; Serial. No, 138,769; filed January I0:, 1950, by us.. In order for the: indicator to measure the radioactivity over the rangesrepresented. by the various scales; and. for." that; bulb.- to. be illuminated. which. has the: same color'a-sthe scalesto be read, arr. automatic rangechanging circuit 23 and a switching system: 2% are provided;

The range-changing circuit 23 includes relays which actuate: switches in: the. switching circuit- 24 illuminate the proper bulb 25. At the same time; the sensitivity of therdetector H is adjusted by the switching: circuit 2 4' so'that theproper indicator scale may be used.

Thetest: circuit shown; in Figure 1. is provided for assurance that: the? above system is functioning properlyandtha't the indicator: t9 is correctly reading: the amount of: radioactivity present. The circuitinc'ludes amntor Zttapair of ganged; manually operated; double-throw switches: 21 and 2t" and a pair of motowdr-iven switches 30 and3 A double pole, double-throw switch may be used instead of the single pole, double-throw switches 21 and 28.

Movable contacts 32 and 33 of switches 2! and 28 are respectively connected to positive and negative lines 34 and 35 of a direct current power supply 36. One stationary contact 3'! of switch 21 is connected to the movable contact 38 of switch 30 and the other contact 39 is connected to a terminal 40 of the motor 26. Likewise, one stationary contact 4| of switch 28 is connected to the movable contact 42 of switch 3| and the other contact 43 is connected to motor terminal 48. The stationary contacts of switches 30 and 3| are connected to terminal 44 of motor 26.

The switches SI] and 3| are operated by cams 45 and 46 (Figure 4) mounted on a shaft 4! driven by the motor 26. The motor is attached as by screws 48 (Figure 3) to a housing 49, and the shaft 41 extends through the housing and is supported at its inner end as by a bracket 50 (Figure 4) suitably attached to the housing. A compartment 56 in the housing is provided as by a partition 58, and an opening '68 in the top of the housing communicates with the compartment. The compartment 56 houses the radioactive specimen when a. calibration measurement is not being made, and when so enclosed the specimen 6 ofiers a minimum amount of interference to the action of the system shown in Figure 2. The ionization chamber is positioned above and to one side of compartment 56 and is fastened to the housing as by brackets 62.

The cams 45 and 46 have lobes 6| and 63, respectively, (Figure 3). The lobes lie above the movable contacts 38 and 42 (Figure 4) of the micro switches 3!] and 3| to press against the contacts and open the switches. The lobes are paced from each other for a reason which will be explained hereinafter. A collar 64 is sleeved on shaft 41 within compartment 56 and is fixed to the shaft as by a screw 66. The collar has thereon an arm 68 supporting a disc attached as by screws 12 to the outer end of the arm.

The disc 10 is so positioned with respect to the ionization chamber |4 that the face H thereof directly faces the chamber, and the axis of the disc lies on the same horizontal plane as the axis of the chamber when arm 68 is in vertical position. In case the timing sequence of the circuit shown in Figure 2 fails to function properly, the rotation of the disc is limited in one direction by a stop 14 (Figure 3) attached to partition 58 and in the other direction by a stop 13 on the housing. A radioactive specimen such as radioactive cobalt is applied as by evaporation to a central pocket in disc face H to form the test specimen 6. The specimen has a long half-life. thereby providing a substantially constant effect on the ionization chamber in its calibrating position.

As previously stated, disc 10 normally rests in compartment 56 so that it offers a minimum amount of interference to the operation of the system shown in Figure 1. Any interference that does take place is constant and therefore can be corrected on the readings of indicator l9 by properly calibrating the indicator.

With disc I0 in its normal position, ganged switches 21 and 28 are in the down or Operate position whereby contacts 32 and 33 touch contacts 39 and 4|, respectively; switch 30 is closed and switch 3| open. As a result, no current flows through motor 26. When it is desired to make a test measurement, switches 21 and 28 are ber.

manually rotated upwards to the Calibrate position. This causes a continuous circuit to be established from power supply 36 through lead 34, contacts 32 and 31, switch 36, terminal 44, motor 26, terminal 40, contacts 43 and 33 and lead 35 back to the power supply.

The motor therefore operates to rotate disc 10 upwardly into the field of the ionization cham- As the motor starts to rotate, cam 46 leaves contact 42 and permits switch 3| to close. After rotating through a predetermined arc, cam lobe 6| moves into position to press contact 38 and open switch 38. This opens the continuous circuit through motor 26 and the motor stops rotating with the disc 10 directly facing the ionization chamber.

Since the radioactivity of disc 10 is a known constant, meter 6 should give a constant reading when the disc is in the Calibrate" position. Although the Calibrate position of the disc has been described as being on a horizontal line with the axis of the ionization chamber 4, it may actually be above or below the axis of the chamber without appreciably afiecting the accuracy of the calibration measurements, provided that proper allowance is made for the change in position.

Preferably the radioactivity of the disc is maintained at a low value for safety reasons, permitting a check measurement to be made only for the low indicator scales, such as scales 20 and 2|. If considered desirable, however, the disc can have a greater radioactivity so that a check measurement may be made for all indicator scales. In such a case, lead plates of varying thicknesses can be placed between the disc and the ionization chamber to diminish the radioactive effect for the calibration measurements on the low scales.

After calibration readings have been taken, the disc 10 may be returned to its position in compartment 56 by rotating switches 27 and 28 downwards to the Operate position. Since switch 3| is closed, a continuous circuit is established which includes the power supply 36. lead 34, contacts 32 and 39, terminal 46, motor 26, terminal 44, switch 3|, contacts 4| and 33 and lead 35. The motor starts to rotate in a direction opposite to that discussed above and, as it does so, cam 45 releases contact 38 and switch 36 closes. As disc Til is returning to its resting position in compartment 56, cam 46 opens switch 3| and the motor stops rotating.

Figure 5 illustrates a modification of the test circuit shown in Figure l. The circuit includes the motor 26, the switches 36 and 2| and a manually operated double-throw switch 86 to which a pair of single-throw switches 82 and 84 are ganged. The stationary contacts 6! and 83 or switch 81] are connected by leads 34 and 35 to the power supply 36 and to the stationary contacts of switches 82 and 64, respectively, and movable contact 85 is connected to motor terminal 40. The movable contacts of switches 82 and 84 are connected to movable contacts 38 and 42 of the motor-driven switches 36 and 3|, respectively. The stationary contacts of the motor-driven switches are connected to motor terminal 44.

When the test circuit is not being operated, switch 86 has its movable contact 85 in engagement with contact 8|, switches 82 and 3| are closed and switches 84 and 36 are open. As a result, no current flows through the motor. To obtain a calibrating measurement, switch 88 is rotated upwardly, causing switch 84 to close and switch. 82. to open. A continuous: 0111011117118 providedfifrom power supplyttithrough leads'sj cone tact'sva3j and 85; terminal 423, motor 26, terminal fllswitch 3d, switch 3 and lead 35 baclct'o the power supply. As the motor" starts to rotate; switch 33! closes. After: the motor has rotated through a predetermined arc, switch-3i opensand the motor stops;

To return. the motor to" its original position; switch 80 is; rotated sothat contact 85 touches contact- 83!. This; causes'switch- 82 to-close and switch 8b to" open, whereby acontinuous circuit is" established which includes power supply 36,, lead: 34", switch 32, switch so: tcr mal at; motor" Z'fii terminal 4b; contacts- 85 and SI of switch 8% and-lead 35-. Sinc'ethe current through the motor is reversed; the motor returns to its original= position, with switch 3' closing at the beginning of. the rotation and. switch as opening at the end of the rotation.

Althoughthisinventionhas beendisclosed and illustrated with referenceto, particular applications, it must be appreciated thatthe principles involved areisusceptible of numerous other applicationswhich will be apparenttopersonasleilled in the art.

Having thus. described the: various features or" the invention, what we claim. as new and desire to secure by Letters Patent is:

1. In an apparatus for testing the ope"ation of a system for measuring the amount of radio activity in a particular locality, an ionization chamber, a radioactive specimen, a motor for driving the radioactive specimen, the motor normally positioning the radioactive specimen out of the field of the ionization chamber, manually operated switching means connected to the motor, and a pair of motor-driven switches operative to stop the motor after a predetermined amount of rotation and prepare the motor for rotation in a reverse direction.

2. In an apparatus for testing the operation of a system for measuring the amount of radioactivity in a particular locality, an ionization chamber, a radioactive specimen, a motor for positioning the radioactive specimen in the field of the ionization chamber, manually operative double-throw switching means connected to the motor, the switching means being adapted in one position to efiectuate a rotation of the motor in one direction and in the other position to reverse the direction of rotation of the motor, and a pair of motor-driven switches operative after a predetermined amount of rotation to stop the motor and prepare the motor for rotation in'a reverse direction upon the operation of the manual switching means. I 3. In an apparatus for testing the? operation of a system for measuring the amount of radioactivity in a particular locality, a specimen having a known amount of radioactivity, *an ionization chamber adapted to convert radioactive emanations into a measurable electric current, a motor for driving the radioactive specimen, the motor normally positioning the specimen out of the field of the ionization chamber, a power source, at least one manually operated switch between the motor and the power source, and a pair of motor-driven switches connected to the power source and so arranged relative to each other that a diiferent switch is closed to stop the motor after a predetermined amount of rotation and to prepare the motor for rotation in an opposite direction. I V

4. In an apparatus for testing the operation of? a system for" measuring the amount of radioactivityin a; particular locality; a' test specimen having a known amount of radioactivity; an ionization chamber, meansa'ssociated with thech'anrber for measuring the radioactivity therein, the test; specimen beingnormally positioned out of the field of the ionization chamber, a motor for moving the specimen intothe fieldof theioni'zation chamber,. a power source, a manually operated switch h'avinga movable contact and a pair of stationary contacts, the stationary contacts being connected to the power; source and the movable contactbeing. connected to the motor; a pair of motor driven switches" connected to. the power source, both switches being closed during the operation of the motor and a different" one of the switches being; opened" at the end of each motor rotation, and a pair of switches connected between the power source" and the motor=driven switches and being adapted to' reverse the.- cur:- rent through the motor upon the operation of the manual switch.

In an apparatus fortesting'tlie operation'of a; system for measuring the amount or" radioac tivity in a particular locality, a test specimenhaving a known amount ofradio'activity, arr ioni zation chamber, means for'measuring the amount of radioactivity'withinthe chamber, a motor; for moving the test. specimen into the field of the ionization chamber so that a calibrating measurement may be made, a power source, a pair of manually operated switches each having a movable contact connected to the power source and a stationary contact connected to the motor, and a pair of motor-driven switches connected to the motor, the motor-driven switches being closed during the rotation of the motor and a diflerent one of the switches being opened after a predetermined time to stop the motor.

6. In apparatus for testing the operation of a system which measures the amount of radioactivity in a particular locality, a test specimen having a known amount of radioactivity, an ionization chamber, means associated with the chamber for measuring the radioactivity therein, the test specimen being normally positioned out of the field of the ionization chamber, a motor for moving the specimen into the field of the ionization chamber, a power source, a pair of ganged, manually operated switches each having a movable contact and a pair of stationary contacts, the movable contacts being connected to the power source, a pair of motor-driven switches, the switches being closed during the operation of the motor and one of the switches being opened after a predetermined movement of the motor to stop its rotation and prepare it for rotation in an opposite direction, and the stationary contacts of the manual switches being connected to the motor and the motor-driven switches to provide for a continuous circuit through the motor in the calibrating position of the manual switches and a reverse current through the motor upon the subsequent operation of the manual switches.

'7. In apparatus for testing the operation of a system for measuring the amount of radioactivity in a particular locality, an ionization chamber, means for measuring the amount of radioactivity penetrating the chamber, a motor, anarm adapt ed to be driven by the motor, a radioactive specimen of known potency carried on the arm and adapted to be driven by the motor tola predetermined position relative to the ionization chamber, a shielded compartment for housing the radioactive specimen in one position of the arm, a pair of motor-actuated switches connected to the motor, each switch being closed during the movement of the radioactive specimen, one of the switches being opened upon the movement of the radioactive specimen into the shielded compartment so as to discontinue the operation of the motor and the other switch being opened upon the movement of the radioactive specimen to the predetermined position relative to the ionization chamber so as to discontinue the operation of the motor, and means operative in conjunction with each of the switches to establish a continuous circuit for driving the radioactive specimen towards the ionization chamber or shielded compartment.

8. In apparatus for testing the operation of a system for measuring the amount of radioactivity in a particular locality, an ionization chamber, means for measuring the amount of radioactivity penetrating the chamber, a rotatable arm, a radioactive specimen of known potency carried by the arm, a motor for driving the arm to bring the radioactive specimen to a predetermined position relative to the ionization chamber to obtain a calibration of the operation of the ionization chamber, a shielded compartment for housing the arm and the radioactive specimen during the times that calibration tests of radioactivity are not being made, a pair of cams adapted to be driven by the motor, a pair of switches controlled by the cams, each cam being positioned to maintain the switches closed during the rotation of the arm, one of the cams being operative upon the movement of the radioactive specimen into the shielded compartment to open its associated switch and the other cam being operative upon the movement of the specimen to its predetermined position relative to the ionization chamber to open its associated switch, and switching means associated with the motor and the cam-operated switches to establish a continuous circuit in one direction through the motor for rotating the arm towards the ionization chamber and in another direction for rotating the arm towards the shield compartment.

IAN H. McLAREN.

CARL E. ALSTERBERG.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,329,280 Lunken et al Sept. 14, 1943 2,340,174 Chance Jan. 25, 1944 2,405,174 Friedman Aug. 13, 1946 OTHER REFERENCES Proceedings of the I. R. E., volume 37, No. 8,

August 1949, pages 913-922. 

